The vertebrae of the human spinal column are commonly classified by position into cervical (neck), thoracic (chest), and lower back (lumbar) vertebrae, with intervertebral discs separating each vertebra from the adjacent vertebrae. In the neck, degeneration of discs often causes vertebrae to undesirably compress their associated spinal nerves, causing uncomfortable symptoms such as pain, numbness, weakness, and disordered reflex symptoms. Degenerated cervical discs may be treated by resection of the discs utilizing a surgical approach through the neck. Once the resection is completed, common procedure is to fuse the vertebrae adjoining the former position of the removed disc. Other conditions which may require fusion include treatment of fractured or broken vertebrae, correction of deformities, treatment of herniated discs, treatment of tumors, treatment of infections, or treatment of instability.
Fusion is a surgical technique in which one or more of the vertebrae of the spine are united or joined to prevent relative movement. The spinal fusion procedure does not directly connect the vertebrae; rather, a bone graft or spacer is positioned between endplates of adjacent vertebrae of the spine during surgery. Over a period of time healing occurs as living bone from vertebrae spans the intervertebral graft and connects the adjacent vertebrae together. Fusion is complete when living bone has completely spanned the graft and the adjacent vertebrae are thus connected by a solid bridge of bone.
Various apparatus are known for retaining vertebrae of a spinal column in a desired spatial relationship so that fusion of the vertebrae can occur. Such known apparatus can include rod or plate systems, with either commonly being attached to the vertebrae with bone screws, hooks, or other structures. For example, anterior fusion of the cervical spine is commonly stabilized using a fixation plate screwed to the vertebrae. The rods and/or plates can be temporary (removed after fusion of the vertebrae is complete) or permanent.
However, currently available plates are generally larger than needed to simply maintain adjacent cervical vertebrae in fixed orientation in most patients. These oversized structures require a relatively large incision and dissection for insertion, which may be complex and time-consuming for the surgeon and require broader dissection of tissues in the neck and greater pressure on tissues being moved out of the way. This generally results in longer healing time and a larger risk of complications in the patient than in a smaller incision and dissection.
Furthermore, the known plates are placed symmetrically with respect to a frontal midline of the spine, and the patient's trachea, larynx, and/or esophagus must be moved aside for access across that midline in the cervical region of the spine. Disturbance of these delicate throat structures often leads to hoarseness, pain, and swallowing difficulties.